In gas turbine engines, barriers or walls, usually called "liners" are installed between the hot exhaust gas flow and surrounding engine material and components in the engine nozzle. For obvious reasons, these liners need to be light--fabricated from thin, but strong materials--to limit engine size and weight. Physical characteristics of this liners can limit their capacity to conduct heat away from local liner hot spots. Attempting to address this, techniques developed in the prior art generally focus on providing uniform liner cooling with forced air.
The liners are exposed to extremely high temperatures, creating unusual expansion problems that often cause liners to warp and buckle to some degree without fatiguing. Liners may contain air passages or metering ports to improve liner cooling, and physical changes, such as warping and buckling, may produce uneven cooling, leading to hot spots.
Typically the liner is cooled with air pumped from engine bypass flow and is directed through holes in a radiation shield into a passage between the liner and the shield. The cooling air exits into the exhaust through the holes in the liner, cooling the liner. U.S. Pat. No. 4,887,663, which is assigned to the assignee of this application, and U.S. Pat. No. 4,800,718 illustrate conventional schemes for constructing improved liners for gas turbine engines. The liner displayed in U.S. Pat. No. 4,800,718 is the type known to employ "louvers" in conjunction with air inlets and air dams. An air duct is shown that includes an up-stream duct wall that terminates in a downstream edge or lip. A second duct wall is spaced radially outward relative to the first surface lip and defines an elongated louver nozzle through which the cooling air that enters the supply orifices (metering holes) exits.
The liner sheet, typically a catenary supported at each end with a hinge pin for easy liner service and removal, may contain a slot extending substantially across the sheet within the field of the air holes, a design found to reduce heat induced mechanical stresses on the sheet. But a problem can arise if exhaust gas flows (reverse cooling flow in effect) through this slot into the passage between the liner and the shield, and it is that to which this invention is directed.